A hydrotreating catalyst may be defined as any catalyst composition which may be employed to catalyze the hydrogenation of hydrocarbon feedstocks. A hydrocracking catalyst may be defined as any catalyst composition which may be employed to catalyze the addition of hydrogen to /massive and complex petroleum derived molecules and the cracking of the molecules to attain smaller molecules. A tail gas catalyst may be defined as any catalyst which may be employed to catalyze the conversion of hazardous effluent gas streams to less harmful products. Such catalyst compositions are well known to those of ordinary skill in the art and several are commercially available. Metal oxide catalysts which come within these definitions include cobalt-molybdenum, nickel-tungsten, and nickel-molybdenum. Also, transition element catalysts may be employed for these purposes. Typical supports for hydrotreating metal oxide catalysts include alumina, silica and silica-alumina supports.
In the past, ex-situ methods of presulfiding supported metal oxide catalysts have suffered from excessive stripping of sulfur upon start-up of a hydrotreating or hydrocracking reactor. As a result of sulfur stripping, an increase in the product weight percent of sulfur is observed along with a decrease in catalyst activity.
The use of high boiling oils, hydrocarbon solvents and mixtures thereof to aid the incorporation of sulfur into a catalyst is not believed to have been previously taught by prior presulfiding methods. Hereforth, a high boiling oil is defined as an oil whose initial boiling point is greater than 400.degree. F.
Hydrotreating and hydrocracking catalysts are typically presulfided by incorporating sulfur compounds into the porous catalyst prior to hydrotreating or hydrocracking a hydrocarbon feedstock. For example, U.S. Pat. No. 4,530,917 to Berrebi discloses a method of presulfiding a hydrotreating catalyst with organic polysulfides.
U.S. Pat. No. 4,177,136 to Herrington et al. discloses a method of catalyst presulfiding wherein a catalyst is treated with elemental sulfur. Hydrogen is then used as a reducing agent to convert the elemental sulfur to H.sub.2 S in situ. Problems arise, however, upon start-up of a reactor due to excessive sulfur stripping.
U.S. Pat. No. 4,089,930 to Kittrell et al. discloses the pretreatment of a catalyst with elemental sulfur in the presence of hydrogen.